The Multiple Functions of Amyloid Beta in the Gut Epithelium and the Role of the Microbiota: A Study in the APP/PS1 Animal Model Subjected to Chronic Synbiotic Treatment.

Background

/ Over the past decade, increasing evidence has shifted attention from the brain to the gut microbiota (MB) as a source and site of systemic dissemination of amyloid-β (Aβ), an APP derivative responsible for plaque formation in the brains of Alzheimer's disease (AD) patients. Furthermore, AD patients and APP/PS1 mice, a transgenic model of AD, exhibit dysbiosis.

Objectives

Using APP/PS1 mice treated from 2 to 8 months of age, we studied ileal and colonic epithelial integrity, intestinal barrier (IB) integrity assessed through tight junction (TJ) protein expression, local immune system, the presence/increase in Aβ expression in enterocytes, and the protective effects of synbiotic treatment.

Methods

The tissue was stained with Periodic Acid-Schiff and Alcian Blue to evaluate epithelial morphology and mucus production, and immunohistochemistry was performed to assess TJs, immune markers, and Aβ expression.

Results

Our results demonstrate that colonic and ileal epithelium of 8-month-old APP/PS1 mice displays IB impairment in term of alterations of goblet cells staining and TJ protein expression and signs of immune involvement. The ileum was more severely affected, showing a reduced epithelial surface area, decreased lysozyme production, and fewer tuft cells. Long-term synbiotic treatment largely prevented APP/PS1 mouse changes and caused a significant increase in Aβ expression in all treated mice.

Conclusions

These findings support the belief in early intestinal involvement in AD and highlight the potential of the microbiota as a target for early intervention aimed at modifying the progression to neurodegeneration. Increased epithelial Aβ labeling after treatment raises the possibility of intestinal management of Aβ, which requires further validation.